DIET, BREEDING SUCCESS, AND NEST-SITE SELECTION OF THE SHORT-TOED EAGLE (CIRCAETUS-GALLICUS) IN NORTHEASTERN GREECE

4 Pages·1994·1.3 MB·English

by  C Vlachos

J Raptor Res. 28(l):39-42
© 1994 The Raptor Research Foundation, Inc.
DIET, BREEDING SUCCESS, AND NEST-SITE
SELECTION OF THE
SHORT-TOED EAGLE
{Circaetus gallicus)
NORTHEASTERN GREECE
IN
Christos G. Vlachos and Nikolaos K. Papageorgiou
Department ofForestry and Natural Environment, Laboratory of Wildlife and Freshwater Fisheries,
University of Thessaloniki, 54006 Thessaloniki, Greece
—
Abstract. Forty-eight pellets of short-toed eagles {Circaetusgallicus) collected during 1988-90 in north-
eastern Greece were examined to determine the eagle’s food habits. The main prey were reptiles (87.2%
by frequency of occurrence) followed by birds (6.9%) and rodents (5.9%). The most common prey species
were Montpellier snake {Malpopolon monspessulanus, 29.4%), grass snake {Natrix natrix, 20.6%), lizards
(Lacerta spp., 18.7%), and European glass lizard {Ophisaurus apodus, 11.8%). Short-toed eagles preferred
to nest in old pines {Pinus brutia, 80% and P. nigra, 20%). Nest trees had a mean height of 12.7 ± 2.9
m, d.b.h. of 43.5 ± 10.9 cm, and age of 85 ± 21.4 yr. The average distance between neighboring active
m
nests was 2200 (range 640-3250 m). Short-toed eagles’ mean breeding success was 0.86 fledged young/
nest.
Key Words: breeding', Circaetus gallicus; food habits', Greece', short-toed eagle.
Dieta, exito reproductive y seleccion de sitios de nidificacion de Circaetus gallicus en el noreste de Grecia
—
Resumen. A traves de cuarenta y ocho egagropilas, colectadas entre 1988 y 1990 en el noreste de Grecia,
se determinaron los habitos alimentarios de Circaetusgallicus. Los reptiles constituyeron la presa principal
(87.2%), sequidos de las aves (6.9%) y de roedores (5.9%). Las presas mas comunes fueron las serpientes
Malpopolon monspessulanus (29.4%) y Natrix natrix (20.6%), los lagartos Lacerta spp, (18.7%) y Ophisaurus
apodus (11.8%). C. gallicus, prefirio nidificar en Ptnus brutia (80%) y P. nigra (20%). Los nidos se
encontraban a una altura media de 12.7 m (DS = 2.9 m), en arboles con un diametro a la altura del
pecho de 43.5 cm (DS = 10.9 cm) y de una edad de 85 ahos (DS = 21.4 ahos). La distancia promedio
m
entre nidos vecinos activos fue de 2200 (rango 640-3250 m). La media del exito reproductivo fue de
0.86 juveniles volantones por nido.
[Traduccion de Ivan Lazo]
A
Short-toed eagle {Circaetus gallicus) food habits serve since 1980 due to its unique raptor fauna.
and nesting habitat characteristics have been re- total of20 birds ofprey breed in the reserve including
ported by Brown and Amadon (1968), Ali and Rip- cinereous vulture {Aegypius monachus), griffon vul-
ley (1968), Glutz von Blotzheim et al. (1971), and ture {Gyps fulvus), imperial eagle {Aquila heliaca),
Massimo (1989). However, such data are not avail- golden eagle {A. chrysaetos) and white-tailed eagle
able for Greece. {Haliaeetus albicilla), making the area not only of
The objectives of our study were to examine the; national but also of international importance.
(1) diet, (2) nest site seleetion, and (3) breeding The reserve covers an area of about 7000 ha and
success of short-toed eagle in northeastern Greece. it is part of a large forest complex of about 40 000
Study Area ha. Vegetation includes Pinus brutia, P. nigra, Quer-
The study was conducted from March 1988 to cus conferta, and (9. cerris. Other species occurring
September 1990 in Dadia Forest, northeastern with lower frequency are Erica arborea, Phillyrea
Greece, which is considered one of the most impor- media. Arbutus andrachne, and Juniperus oxycedrus
tant breeding areas of short-toed eagles in the coun- The climate is mediterranean with dry summers
try (Hallman unpubl. data). Dadia Forest is located and rainy winters. During March to September
between 40°59'-4ri5'N and 2H9'-2'’36'E. It lies (breeding season for short-toed eagle) the mean
m
from 50-800 above sea level. monthly temperature was 19.4°C with minima and
The study area has been declared a wildlife re- maxima of 8.9°C (March) and 27.6°C (July), re-
39
40 Christos G. Vlachos and Nikolaos K. Papageorgiou VoL. 28, No. 1
Table 1. Composition of pellets (A^ = 48) found in short- 1989). The abundance of reptiles was estimated using
toed eagle nests in northeastern Greece. transects in different biotopes. In total 18 transects (100
m H
X 5 each) were used and were counted at 1000 and
1700 H.
Number Frequency The height, age, and diameter breast height (DBH) of
OF Indi- OF Occur- the nest tree, and the height of the nest, the diameter of
viduals rence the branch where the nest was placed, and the distance of
Species M % the nest from the trunk were recorded for each nest tree
The nesting habitat was determined by vegetation analysis
Reptiles within a plot 50 x 20 m centered on the nest.
Malpopolon monspessulanus 30 29.4
Matrix natrix 21 20.6 Results
Matrix tesselata 4 3.9 A
Diet. total of 48 pellets were collected during
Elaphe situla 2 1.9
the 3-yr study period. The results of the analysis
Vipera amodytes 1 0.9
Ophisaurus apodus 12 11.8 are presented in Table 1. The data show that short-
Lacerta sp. 19 18.7 toed eagles’ main food group by frequency of oc-
currence was reptiles (87.2%) followed by birds
Birds 7 6.9
(6.9%), and rodents (5.9%). Reptile density varied
Mammals
considerably among the biotopes (Table 2). The main
Apodemus sylvaticus 6 5.9
period of reptile abundance in our study area starts
Total 102 100.0
from the beginning of April to the end of September.
spectively. The mean monthly precipitation during
mm
the above period was 40.6 with minima and Nesting Sites. Eighty percent of the short-toed
mm mm
maxima of 0.0 (August) and 52.4 (June), eagle nests found in the study area were in Pinus
respectively. brutia and 20% in Pinus nigra. Nest tree height was
Methods much less variable than age and DBH. Short-toed
eagles preferred old pines with mean height of 12.7
The diet of the short-toed eagle was determined by DBH
± 2.9 m, of 43.5 ± 10.9 cm and 85 ± 21.4
analysis of pellets found in the nests. Active nests were
located at the beginning of the breeding season and were yr of age. Nests were located on branches with a
visited at irregular intervals to collect regurgitated pellets. mean diameter of 13.5 ± 3.3 cm and a mean distance
Most pellets were collected after the hatching ofthe chicks from the trunk of 1.4 ± 0.3 m.
to avoid disturbance at the nests.
Vegetation analysis around each nest tree revealed
The identification ofreptile prey was accomplished with
a scale key (Papageorgiou et al. 1993). Mammals were that nest-site habitats selected by short-toed eagles
identified using a hair key (Papageorgiou and Sfougaris were forest stands with open canopy (40-60%) and
Table 2. Density of reptiles in different biotopes in Dadia Forest (individuals/ha).
Noninten- Shrubland
sively WITHIN
Cultivated Cultivated Dense Pine Open Pine Degraded
Species Land Land Rangeland Forest Forest Oak Forest
Malpopolon monspessulanus 1 3 2 —1 2 1
Ophisaurus apodus 1 3 1 — —3 2
Matrix natrix —6 —3 1 — 2
Vipera amodytes — —1 — —1 1
Coluber najadum
1 — 1
Lacerta viridis 4 13 10 — 4 14
Lacerta trilineata —2 9 4 — —2 8
Lacerta praticola — —5 —2 — — 6
Podarcis taurica 3
Total 14 37 21 1 12 38
March 1994 Short-toed Eagle Biology 41
Figure 1. Annual breeding cycle of short-toed eagle in Dadia Forest.
with the nest tree being the dominant one. The nest- neuver through closed stands and the potential of
ing sites were located at an elevation ranging from open habitat to support a high density of reptiles.
50-600 m. The average nearest distance between The high population density of the short-toed ea-
neighboring active nests was 2.2 ± 0.48 km. gle in the Dadia Forest (1 pair/1370 ha) and the
Breeding. The breeding cycle of short-toed eagles observed high breeding success indicates that the
is given in Fig. 1. The eagles arrived on the study Dadia Forest’s potential for food production and
area at the end of March and the laying period began nesting sites is adequate to meet the short-toed ea-
between 10-20 of April. The hatching date, after an gle’s requirements. This conclusion agrees with Hel-
average incubation period of 47 d, was estimated to mer and Scolte (unpubl. data) who reported that the
be the beginning ofJune. The breeding pairs, clutch northeastern part of Greece supports the highest
size and breeding success of short-toed eagles is pre- reptile density in Europe. The main period of reptile
sented in Table 3. All young that hatched were reared abundance in Dadia Forest coincides with the breed-
successfully.
Discussion
Our results on the diet of short-toed eagle agree Table 3. Breeding success of the short-toed eagle in
northeastern Greece.
with previous research elsewhere (Boudoint et al.
1953, Brown and Amadon 1968, Glutz von Blotz-
heim et al. 1971). The staple diet of short-toed eagles Number Number Number
OF Number OF Hatch- OF Fledg-
consists of reptiles, occasionally supplemented with
Breeding OF lings/ lings/
birds and rodents.
Year Pairs Eggs/nest Nest Nest
Short-toed eagles prefer breeding areas with dry
and warm climate and open discontinuous forest 1988 10 1 0.8 0.8
stands and open habitat. The selection of such hab- 1989 12 1 0.92 0.92
itat reflects the short-toed eagle’s inability to ma- 1990 11 1 0.91 0.91
42 Christos G. Vlachos and Nikolaos K. Papageorgiou VoL. 28, No. 1
ing cycle of short-toed eagles, therefore contributing Vol. 4. Academische Verlagsgesselschaft, Frankfurt am
to successful rearing of young. Main, Germany.
Massimo, B. 1989. Status del Biancone {Circaetus gal-
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